1. Field of the Invention
This invention relates generally to the directed self-assembly (DSA) of block copolymers (BCPs), and more particularly to the DSA of BCPs to make an etch mask for pattern transfer into a substrate.
2. Description of the Related Art
Directed self-assembly (DSA) of block copolymers (BCPs) has been proposed for making imprint templates. Imprint templates have application in making patterned-media magnetic recording disks and in semiconductor manufacturing, for example, for patterning parallel generally straight lines in MPU, DRAM and NAND flash devices. DSA of BCPs by use of a patterned sublayer that provides a chemical contrast pattern for the BCP film is well-known. After the BCP components self-assemble on the patterned sublayer, one of the components is selectively removed, leaving the other component with the desired pattern, which can then be used as an etch mask to transfer the pattern into an underlying substrate. The etched substrate can be used as an imprint template.
In conventional DSA by use of a chemical contrast pattern, an array of sparse guiding lines, usually made of a cross-linkable polymer mat, is lithographically patterned on the substrate. The pitch of these guiding lines (Ls) needs to be an integer multiple of the natural pitch (L0) formed by the block copolymer to be directed, i.e., Ls=nL0, where n is an integer equal to or greater than 1. However, the width of the guiding lines generally needs to be about 0.5 L0, or nearly equal to the width of one of the block copolymer components. While lithographic applications benefit from the fact that the guiding lines can be sparse (at a pitch of nL0) and that the high density comes from the density multiplication afforded by the block copolymers, the resolution requirement to pattern the width of the guiding lines keeps scaling with the final block copolymer dimensions. As lithographic applications advance to smaller dimensions, especially below 20 nm full pitch, the fabrication of guiding lines with a width below 10 nm while maintaining adequate roughness and width uniformity becomes ever more difficult and beyond what is possible with current resist materials for electron-beam (e-beam) or optical lithography.
What is needed is a guiding pattern for DSA with a width larger than the half pitch of the final block copolymer pattern to make it easier to fabricate the etch mask.